1. Field of the Invention
The technical scope of the invention is that of firing safety devices for pyrotechnic devices.
2. Description of the Related Art
Safety devices (or SADs) are well known. They generally incorporate a barrier blocking a transmission channel which connects an igniter to a pyrotechnic charge.
The barrier thus positions itself in the way of the flame between the igniter and the charge thereby preventing the priming or firing of the latter.
Patents FR-2650662 and FR-2801099 thus disclose such known safety devices.
One of the problems encountered with these devices is their encumberment. The parts are relatively solid to ensure the interruption of the pyrotechnic train. The motor means enabling the barrier to be displaced must thus be powerful. More often than not, it is springs which are used, such springs remaining tensed during the storage phases possibly leading to a deterioration of their mechanical properties and a reduction in arming reliability.
Small electric motors may be used, but these are cumbersome, fragile, difficult to integrate and require a substantial power source.
For the last few years, it has been proposed to make all or part of safety devices using chips incorporating electro-mechanical elements micro-machined or micro-engraved either on or in an element applied to a substrate or directly on or in the substrate itself. This technology, known under the name of MEMS (Micro Electro Mechanical System), indeed enables us today to manufacture micro-devices by implementing a technique close to that used in the manufacture of electronic integrated circuits.
Patents EP-1559986 and U.S. Pat. No. 617,650 disclose such safety devices.
However, to date this technique is only implemented to manufacture electric contacts or barriers enabling an optical firing signal to be interrupted, or else projectable elements for igniters (“slapper” type detonators).
Such barriers are not directly positioned between the pyrotechnic igniter and the charge, and the interruption of the pyrotechnic train is not ensured.
Patent EP-1189012 discloses a miniature safety device in which a transmission channel receives an igniter. This channel is blocked, firstly by a first barrier held in place by a lock, and secondly by a second barrier, transverse to the first one, and able to slide via the action of an actuator.
The dimensions of such a device are relatively large since the igniter has substantially the same diameter as the transmission channel. Moreover, the pyrotechnic charge ignited by this device is positioned in a direction perpendicular to the plane of the barrier and can only be ignited through a transverse slot in the second barrier and after both barriers have been moved.
Such a device is both complicated and relatively cumbersome. The energy supplied by the igniter is partly used to unlock and move the barrier. The residual energy alone is used to ignite a pyrotechnic composition. Such a principle gives rise to malfunctions and is unreliable.